Pad Printing

How does pad printing work?

Please see our excellent Introduction to Pad Printing, available on the web (or call customer service to request a copy).

Is pad printing easy, like making a photocopy?

According to our customers, pad printing is more difficult than photocopying and slightly easier than screen printing. It incorporates some old-world principles, as well as many new technological improvements that make it more of a science now than the old idea of it being an “art”. The successful pad printing machine operator will be a bit of a technician at heart that follows procedures and recipes carefully.

How do I determine if pad printing is the best way to mark my product?

As with any other technology, you must weigh its benefits and limitations against your project’s requirements to determine if you have the right match. We at Printex are always available to discuss your application with you in a plain English no-nonsense fashion.

If we have recommended pad printing to you, rest assured this is the best way (and possibly the only way) to mark your product effectively.

How do I select the right Printex machine for my application?

The primary criteria for selecting equipment are: image size, overall part size and geometry, the print position(s) per part, the number of colors per image and the number of parts per minute (or day) required. With any application, there is likely to be more than one equipment model which will accomplish the task. For most first-time pad printers, choosing the right machine is a daunting task. We at Printex routinely evaluate current and possible future applications for our customers and provide a written quotation for the recommended equipment.

Could I run my pad printer as fast as I want?

Cycle times vary widely, with a handful of interdependent factors. Most machine manufacturers (Printex included) quote top machine speed in their literature and specifications. Actual printing rates will depend as follows:

Inks.
Pad printing inks dry quickly, but not instantly. Even inks that are designed to print “wet”, need a short gel time before being transferred in order to obtain acceptable results. This time window will vary with climatic conditions, ink type, plate depth, coverage, etc. The time could be as little as one second to as much as 8 seconds or more. Typically, it is 3-4 seconds without forced acceleration, such as air flow or heat.

Pads.
Being a soft, three-dimensional shape, large pads may tend to vibrate at higher machine speeds. Vibration during ink pickup or transfer will yield unacceptable print results, so the machine must be slowed to allow the pads to remain steady. Additionally, pads that compress over a large print area will offer some resistance to machine movements, slowing the cycle further.

Operator and/or Auxiliary Operations.
Just how quickly can an operator load and unload your parts without fumbling? Must the operator stop periodically to move trays of parts, open boxes, or perform some other necessary function? What about upstream or downstream operations with which you must synchronize your pad printing process?

These are some of the elements that will actually determine in real time the speed at which you could run the machine.

Can pad printing machines print with other fluids besides ink?

Yes. In addition to cosmetic ink markings, pad printing has been used to apply conductive materials, lubricants, solder paste, wax, adhesive coatings, biomedical chemicals and more. The pad printer does not care what media it is transferring, as long as it meets a few basic criteria:

  • The viscosity is similar to pad printing inks.
  • The material is cohesive (does not bead up or lose its shape when lifted out of the plate).
  • The material is reasonably homogenous (does not separate or precipitate).
  • The material transfers onto the pad, rather than stick to the printing plate.
  • The material sticks better to the target object (substrate) than to the printing pad.
  • The material does not corrode the printing plate, attack the pad or machine parts.

We do not intend to make this sound easy. Printing of specialty fluids requires much testing and validation, but most times can be done.

Is pad printing good for applying serial numbers or date/lot codes?

Possibly – it depends upon the frequency at which the variable information changes. Serial numbers typically change with each individual part. Since pad printing is a printing plate-based process, this would require a new printing plate to be made for each part, or a re-adjustment of pad and part position which is impractical. Date codes and lot numbers may change after several hundred or several thousand parts and therefore may be feasible with pad printing, using relatively inexpensive photopolymer plates. One must weigh the cost of a printing plate and the down-time required to change the plate in the machine when considering this method.

Could I pad print very large images or objects, such as a 10

Possibly, but you are advised to explore other methods of marking or labeling for those items. Printex has produced pad printing machines large enough to print the control panels on barbecue grills and an 8.5″x11″ sheet with 100% coverage. Due to the nature of pad printing, these machines and the printing pads they utilize are necessarily very large and expensive. They apply hundreds of pounds of pressure to the part during printing. On the other hand, screen printing can be used to easily print poster-sized flat items with relative ease, and it is (by comparison to pad printing) a simple matter to apply a label to the side of a 55-gallon drum. As you may have gathered, pad printing is most efficient for smaller items and images.

Can pad printing reproduce photographic images?

Yes, in both black-and-white and full color. The pre-press preparation is a little different than what is required for standard spot printing. Photo-quality pad printing is among the most challenging of pad printing applications, particularly when attempting a high-resolution reproduction, but the results can be quite impressive.

Could I pad print parts while they are moving on a conveyor?

No. Standard pad printing requires that the part be stationary and secured during the ink transfer.

When pad printing multi-color images, does the ink have to dry between colors?

No. Pad printing inks are designed to be fast drying, and their drying speed is enhanced by the thin ink film layer therefore, “wet-on-wet” multi-color pad printing is possible. In practical use, best results are usually achieved with moderate cycle times. Occasionally the use of air flow across the pads or printed parts to accelerate the evaporation (flashing) of solvents from the printed ink is necessary.

Could I mount my Printex sealed inking pad printer sideways or upside down?

Generally no. Sealed Inking Pad Printers are designed to operate upright. The Sealed Ink Cup works on the principle of gravity. Gravity pulls the ink down into the artwork etching on the plate. However, Printex offers the RP-machine series and potential modifications of the same as a solution for vertical and upside-down printing.

Could I incorporate pad printing on a machine that performs other work as well?

Yes, as long as the basic requirements of pad printing are met. Printex provides solutions to mate with existing automation, and can design and manufacture custom systems which incorporate pad printing with pre- and post-print secondary operations. If you have a need for this service, please fill out and send our electronic quote request form, and we will contact you to discuss the detail.

Pad Printing Machines

Do I have to buy supplies from my machine vendor?
In most cases no. Many supplies are cross-compatible, with a few exceptions as noted below:

Inks: certainly the quality and performance of inks for a particular application can vary from brand to brand, but as a general rule, pad printing ink is pad printing ink. Quality, performance and price are important issues, but so are availability, support and service. Printex will gladly help you evaluate your ink needs and recommend the best product for the job, even if we do not carry it.

Plates: Photopolymer plates are easily cut to any size and supplied processed or unprocessed. Printex strives to provide superior service for your plate needs, we carry the best materials directly from the best manufacturers in the world.

Pads: much like inks, a pad is a pad, though once again quality and performance can vary. The main issue with pads, is the method by which they are mounted to the machine.
This can vary by manufacturer. Printex pads are as cross-compatible as possible in this respect.

Doctor Blades, Sealed Ink Cups and Miscellaneous: doctor blades usually boil down to thickness and width, the material comes in strips and can be cut also to length.
Printex open-well machines use standard strips of doctor blade material, we have these available in-stock in several thicknesses, finishes and widths which can be cut to any size.
Printex sealed ink cups are only compatible with Printex sealed ink cup machines.

Pads

How long do printing pads last?
The life of a pad will vary greatly depending upon its durometer, the conditions of use, the aggressiveness of ink chemistry and the nature of the substrate being printed. On the average, a pad can last at least 30,000 cycles. A working life of over 100,000 cycles is possible in some cases.
Do pads yield consistent results throughout their lifetime?
Printex pads are made with the best silicone materials available and do not require a “break-in” period. As pads age, the integrity of the image transfer will tend to degrade, evidenced by a slightly fuzzy image, particularly in areas of fine detail. A pad can be used as long as one deems the results to be acceptable.
What is the correct way to clean a printing pad?
New pads should be gently wiped with a soft, lint-free rag which has been dampened with C-Solv, lacquer thinner or ink thinner. This will remove any surface excess oils, and assist with immediate ink pickup and transfer. During its service life, the pad should be cleaned using the sticky side of clear packing tape to lift dried ink and dirt off of the working surface of the pad.
What is the significance of a pad's durometer?
Durometer is the relative hardness of the silicone rubber of which the pad is made. Printex offers three standard durometers and can supply many more ranging from 0 to 75 durometer by special order. General rules for the effects of durometer can be found in our introduction to pad printing.
What is the correct way to store a printing pad?
Pads should be stored in a cool, dry place, away from exposure to direct sunlight, dust and debris. The pad should be rested on its base (inverted), and under no circumstances should the working surface be in contact with other objects, as permanent dents or creases could result.

Plates

How do I choose between photopolymer plates and steel plates?
Service life is the primary factor in determining which type of plate to use. Steel plates last several hundred thousand life cycles and are more expensive than photopolymer plates. Photopolymer plates have a relative life of 20,000 to 60,000 cycles and cost considerably less than steel plates. A steel plate is a good choice for an image that you know will be used indefinitely and repeatedly. Photopolymer plates are excellent for short-run work, where frequent image changes are common, or for do-it-yourself customers.
Photopolymer Types
“Water” and “alcohol” refer to the solution in which the exposed photopolymer plates are developed. Due to environmental pressures, manufacturers of plate materials have develop effective water-based systems. The rising cost of shipping and handling alcohol-related developers from the Department of Transportation (DOT) after 9/11 make using alcohol developing plates less and less cost effective.

In earlier times, alcohol plates represented the better products, now this is no longer the case. At this point, Printex G2-73 water developing photopolymer plate material is superior to other materials carried by Printex or in the marketplace. Plus, there are some alcohol-based inks which will dissolve alcohol-based plates. In this case, the advantage of water-based plates becomes even more obvious.

Could I make my own plates?
For photopolymer plates, the answer is yes. Printex offers our UVAC photopolymer plate exposure units and related supplies for end-user plate making. Printex also offers both inkjet and laser artwork films, chemistry to support end-user plate making in addition to technical training and support. Manufacturing steel plates requires specialized equipment and the use of corrosive chemicals. For these reasons, Printex does not offer a do-it-yourself steel plate system.
I make my own polymer plates. How do I know if they are right?
A good plate is characterized by a crisp image area which is uniform in appearance, uniformly clean and smooth non-image areas and an etch depth yielding good ink opacity. Examine your plates for streaks, processing brush marks, voids in the image and “pimples” (high spots) in the image. Also, examine the screen pattern in the image areas of the plate under magnification to ensure that the screen is uniform. If all appears well, the only remaining issue is depth of etch. Try printing with the plate to check the opacity and relative wetness or dryness of the print and adjust the second exposure as needed.
What do I use to clean a plate?
For photopolymer plates, use C-Solv, ink thinner or lacquer thinner. NEVER USE THE DEVELOPING CHEMISTRY TO CLEAN A PLATE. Steel plates should be cleaned in the same way. Additionally, steel plates should be coated with a rust inhibitor to prevent oxidation.

Cups

What is the difference between open ink well and sealed inking machines?
Sealed inking systems employ a hermetically sealed container (ink cup), which acts as the ink supply, flooding and doctoring mechanism all in one. The seal is accomplished using a ceramic ring with a highly polished working edge. Advantages are: stability of ink viscosity, long plate life, easier cleanup compared to open well systems, cleaner operation, and when using one-component inks, the printer can be left set up over night. Disadvantage is: larger plate sizes are necessary to accommodate ink cup travel.

Open ink well systems (older technology) use a trough (ink well) for the ink supply, located behind the printing plate. A flood bar pushes a pool of ink over the plate, and a doctor blade removes the ink from the plate surface, leaving ink on the etched artwork area ready for the pad to pick up. Advantages are: typically smaller plate size relative to the image area. Disadvantages are: the ink supply is exposed to the air and must be frequently adjusted due to thinner evaporation, fume emissions are much higher than with sealed inking systems, open inking systems are not as clean–the inking system must be completely cleaned at the end of each production day and plate life is much shorter due to the doctor blade abrasion.

Do I have to completely fill my Printex sealed ink cup with ink?
In most cases, yes. In any case, we do not recommend that you fill the cup less than halfway. Due to inertia, the ink inside the cup takes on a wave action as the cup moves back and forth. For example, as the cup moves forward, the ink in the cup tends to pile up against the backside of the cup, leaving the front edge dry.

When the cup comes to rest for several seconds, the ink settles down again. If your machine is running quickly (most machines are), the ink may never fully recover from each “wave” as regions of the engraved image will always be in the dry zone. As you probably know, if the engraved image does not get completely flooded with ink, you will not get repeatable good print results.

Could I use a smaller ink cup than the one that came with my Printex machine?
Yes. Printex sealed inking pad printers can accept any of our standard ink cups, up to the maximum size cup provided with the machine. When printing a relatively small image, a smaller cup can be used to reduce the amount of ink needed.
What is the best way to clean my Printex sealed ink cup?
Step 1: Printex G3 cups are coated with a patented non-stick material making cleaning fast and easy. The ink cup should be carefully emptied by allowing it to drain and the remaining ink stored for future reuse. If two-part ink is used, it needs to be placed into a holding container for future proper disposal (please consult your federal, state and local rules and regulations). Never dispose of ink by discarding it as garbage.

Step 2: After a few minutes of draining, place the cup into a container filled with Printex D-Solv (or other suitable cleaner) to soak for a few minutes.
After that time, the ink should be emulsified enough for it to be cleaned off easily with a bristle brush while the ink cup is still immersed in D-Solv.

Step 3: After you’ve brushed out all the emulsified ink, and made sure that there is no ink left, take the ink cup out of the container of D-Solv, and rinse it off in warm water. Use forced air to dry the ink cup.

Inks

Are pad printing inks available in any color I want?
Printex inks (made by Sigma Ink Corporation) come in over thirty standard colors. Twelve of those colors compose a Pantone color matching system which can be used to reproduce any of the Pantone coated series colors, well over 1,000 colors total. Our customers can purchase this system to do their own color blending. In addition, Printex can provide custom color formulations. We can also blend some Day-Glo colors, metallized and perlescent colors. Metallic pad printing inks look like metallic paint, lacking the luster of foils, and limited by their particle size availability suitable for pad printing.
How do I determine what type of ink to use?
Printex has an applications table called Substrate Compatibility Chart to recommend a suitable ink for most common substrates. When in doubt, test it out, or simply contact our Customer Service or Technical Support team to send us your sample part to test at our Headquarters in Poway. This way we can provide you conclusive results free of charge.
What about the environmental impact of pad printing inks?
Pad printing inks are solvent-based, are considered paint-related materials by the Department of Transportation (DOT) and the Environmental Protection Agency (EPA). The solvent content means that they are flammable and they release Volatile Organic Compounds (VOCs) into the atmosphere. These inks must be handled shipped and stored properly. Disposal must be handled in the proper manner according to all applicable regulations. See our Material Safety Data Sheets (MSDS) for more information.

The advent of sealed inking systems (as featured in Printex machines) has greatly reduced VOC emissions on the pad printing press.

What does hardener (catalyst) do to the ink?
Hardener, which is also known as catalyst, reacts (cross-links) with ingredients in the ink to polymerize it. Practically speaking, this is usually done to make the ink adhere to a substrate. It also makes fully dried and cured ink more resistant to scratching, rubbing and solvents. Hardener can only be used in an ink that is designed to work with it. A result of using hardener with ink is a limited working life (pot life) once blended. After use, the cup must be cleaned, and the remaining ink must be disposed of.
Could I mix different brands or series of inks and thinners together?
Some ink series “share” their thinner systems but it is not recommended to mix various manufacturers inks and thinners without conducting conclusive tests as to the behavior and results of this mix. Printex knows from experience that blending Sigma inks with anything other than Sigma thinners (of the same series) will result in unpredictable performance. Certain third-party pigments and additives will work in some pad printing inks, but it is always best to consult your ink supplier before trying.
How much thinner should be added to pad printing ink? Can I omit the thinner?
There is an exact amount of thinner that should be added to Sigma pad printing inks prior to use. Typical for most applications is 15%-30% thinner to ink batch weight ratio measured by weight and mixed thoroughly. Depending upon the application, the amount of thinner could be as little as 10%, and as much as 35%. As a general rule, fine/small artwork and half-tones require a higher than 30% thinner ratio. Inversely, with large solid fills and bold lines, 15-20% will be correct. Too much thinner will result in a pale, spotty print. All pad printing inks have to be blended with some amount of thinner, as they come in concentrated form.
How much ink does pad printing consume?
This varies by the nature of the artwork being printed, but in any case the answer is: next to nothing. Ink consumption could actually be measured by printing a part with the image, weighing the printed part using an extremely sensitive scale, and comparing that weight to the unprinted weight of the same part. A scale with 0.001 of a gram sensitivity would be the minimal required for such a test. Even if such a device were available, the results would still be approximate, because it would not take into account factors like: solvent evaporation, ink loss during plate changes, cleaning and pot life which all contribute to ink consumption.
What is retarder used for?
Retarder is a type of thinner with a very slow evaporation rate. It is used to extend the evaporation (flashing) time of the ink and counteract premature drying. Typical reasons for using retarder would be very hot and/or dry climatic conditions, a slow machine cycle time, or the need to reproduce very fine details (which tend to dry quickly on the printing plate). Retarder should be added carefully in small amounts, as a little retarder tends to have a big effect on ink dry time. Since retarder also acts as a thinner, it lowers the viscosity of ink just like regular thinner. When it is needed, it should be used in lieu of the same amount of the thinner content. Under most conditions, the amount of retarder needed will not exceed 15% ratio.

Substrates

Could I print on very delicate or flexible items?
The transfer pad applies some pressure to the part being printed. The object must be supported so that it does not flex or shift during printing. Printing a sheet of paper or thin plastic (flexible) is easy, since it can rest on a flat surface. Printing an eggshell, a delicate wine glass, or a Christmas ornament is more challenging and requires special printing pads and fixture tooling. As we frequently say: when in doubt, consult with us.
What are the easiest materials to pad print?
Thermoplastics such as styrene, acrylic, polycarbonate, vinyl, butyrate and blends of those plastics (such as ABS and PVC), wood, paper and lacquered surfaces are among the “easiest” materials to pad print, meaning that they readily accept popular single-component inks.
Could I pad print all the way around a cylinder or sphere?
Sometimes, yes. In conventional pad printing, the image is normally transferred to the desired object in a straight, downward stamping motion. The laws of physics limit pad printing of a compound curve (sphere) or cylindrical object to 30% (120 degrees) coverage (wrap). There is a variation on standard pad printing, in which the artwork designed to wrap around an object is picked up by the pad as flat art, and then the object is rolled across the surface of the pad. This effectively wraps the artwork around the part. The primary limitation of this method is width–the technique works best with narrow bands or stripes.
What are the most difficult materials to pad print?
Silicone rubber and/or silicone coated surfaces, Teflon, nylon, PP/PE and Santoprene are among the most difficult materials to print. Most of them are designed to resist adhesion, and therefore require special inks and possibly special pre-treatment before printing.
Could I print on items that are greasy or covered with mold release?
No. Substrates need to be free of all surface contaminants in order for the ink to adhere properly. In some cases, the substrate may be cleaned with alcohol.
Can pad printing machines print on anything?
Virtually – which means, “we’d say absolutely, except for these little things…” By its very nature, pad printing requires that the ink stick better to the item to be printed than it does to the pad. Otherwise, the ink will not transfer properly. Ink formulators have come up with some chemicals for this problem, but there is a wealth of materials out there that are specifically designed to resist bonding with anything. This rules out printing on greasy or wet surfaces, Teflon and other “non-stick” substrates (some ink may transfer, but in all likelihood it will flake or rub right off). Being a contact printing method, pad printing applies pressure to the substrate, and this usually forbids pad printing extremely fragile objects. Finally, pad printing inks are affected adversely by extremes of temperature and humidity. Frozen objects and heated objects are not suitable.
Could I print on painted or coated items?
In most cases, yes. As with any pad printing application, testing is paramount. Paints such as lacquer, enamel and powder-coatings are pad printable, as are shellac, urethane and most other clear-coats. Some UV, and hard coatings are not suitable for pad printing due to extremely low surface tension.
Could I pad print into seamlines, stepped levels, grooves or corrugated textures?
The answer to this question is a very guarded “maybe.” The success or failure of this will largely rest on the geometry of the part, the textures and details within it. The only way to provide a definite answer is case-by-case, through testing.
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